let obj = {
	name: '许嵩',
	num: 25
}

const singer = [{
		name: '周杰伦',
		num: 20
	},
	obj,
	{
		name: '林俊杰',
		num: 19
	},
	{
		name: '蔡徐坤',
		num: 10
	},
	{
		name: '鹿晗',
		num: 0
	},
]

const nums = [1, 2, 3, 4, 5, NaN]

Array.prototype.my_includes = function(val, start = 0) {
	if (start < 0) start = this.length + start
	const isNaN = Number.isNaN(val)

	for (let i = start; i < this.length; i++) {
		if (this[i] === val || (isNaN && Number.isNaN(this[i]))) { // NaN === NaN
			return true
		}
	}
	return false

}

const res = nums.my_includes(NaN, 0)

console.log(res);
